This invention relates generally to composite constructions comprising a hard material phase and a relatively softer ductile material phase and, more particularly, to composite constructions having ordered micro and macrostructures of polycrystalline diamond and a relatively softer ductile material to provide improved mechanical and/or thermal properties, when compared to traditional constructions formed from polycrystalline diamond alone.
Polycrystalline diamond (FCD) and polycrystalline cubic boron nitride (PCBN) constructions, synthesized by high temperature/high pressure processes, are well known for their mechanical properties of hardness and wear resistance, making them a popular material choice for use in such industrial applications as cutting tools for machining, mining and drilling where such mechanical properties are highly desired. For example, PCD and PCBN constructions are provided in the form of surface coatings on, e.g., inserts and shear cutters used with cutting and drilling tools to impart properties of hardness and wear resistance thereto.
Traditionally, such PCD and PCBN inserts and shear cutters are formed by coating a carbide substrate with one or more layers of PCD or PCBN. Such inserts and shear cutters comprise a substrate, a surface layer, and often transition layers to improve the bonding between the coating and the substrate. The substrate is, most preferably, a carbide substrate, e.g., cemented carbide, tungsten carbide (WC) cemented with cobalt (WCxe2x80x94Co). The coated layer or layers of PCD conventionally comprises a binder metal content from 10% to 30% by weight to facilitate intercrystalline bonding and bonding of the layers to each other and to the underlying substrate.
Binder metals used to form PCD include cobalt, iron, nickel and/or mixtures or alloys thereof, and can include other metals such as manganese, tantalum, chromium and/or mixtures or alloys thereof. However, while higher metal content typically increases toughness, higher metal content also decreases hardness, thereby limiting the flexibility of providing coatings with the requisite properties. Additionally, when variables are selected to increase hardness, typically brittleness also increases, thereby reducing the toughness of the cutting element.
Generally, PCD and PCBN each exhibit extremely high hardness and provide a high degree of wear protection to a cutting element. However, in more complex wear environments causing impact and fretting, layers comprising PCD and PCBN are known to fail by gross chipping and spalling. For example, inserts coated with a PCD monolayer are known to exhibit brittleness that causes substantial problems in practical applications. Conventional methods of improving the performance of PCD or PCBN layers include controlling particle size to maximize toughness, but the effect is limited.
It is, therefore, desired that PCD and PCBN composite constructions be provided that are specifically designed to have improved properties of fracture toughness, impact resistance and/or fatigue life when compared to conventional PCD and PCBN constructions, thereby reducing the potential for conventional PCD and PCBN failure modes of spalling and/or chipping. It is desirable that PCD and PCBN composite constructions have such properties of improved fracture toughness, impact resistance and/or fatigue life without sacrificing other desirable properties of wear resistance and hardness associated with the PCD and PCBN materials. It is desired that such composite constructions be adapted for use in such applications as cutting tools, roller cone bits, hammer bits, drag bits and other mining, construction and machine applications where properties of improved fracture toughness, impact resistance and/or fatigue life is desired.
PCD and PCBN composite constructions of this invention have an ordered structure of two or more material phases that are combined together in a packed or woven configuration to provide improved properties of fracture toughness, impact resistance and/or fatigue life when compared to conventional PCD and PCBN constructions. Specifically, composite constructions of this invention have a structure of two or more different material phases that are interwoven or that are packed together.
In an example embodiment, one of the material phases is formed from materials selected from the group consisting of: polycrystalline diamond, polycrystalline cubic boron nitride; carbides, borides, nitrides, and carbonitrides from groups IVA, VA, and VIA of the Periodic Table; and mixtures thereof. Another of the material phases can be formed from a material having a degree of ductility that is higher than that of the first material phase. Example second material phase materials include those selected from the group consisting of cermets, Co, Ni, Fe, W, Mo, Cu, Al, Nb, Ti, Ta, and mixtures thereof.
Preferred embodiments of composite constructions of this invention comprise: (1) a first material phase formed from WCxe2x80x94Co, and a second material phase formed from Co; (2) a first material phase is selected from the group consisting of polycrystalline diamond, polycrystalline cubic boron nitride, and mixtures thereof, and a second material phase being a cermet material; and more preferably (3) a first material phase formed from polycrystalline diamond and a second material phase formed from WCxe2x80x94Co. Alternatively, the material phases can be formed from the same types of materials, differing in the proportion of the material used in each material phase.
Woven or packed composite constructions of this invention have surface structures formed from a number of the order material phases (made from the same, similar, or different materials) that are specifically engineered (in terms of geometry, arrangement, and materials) to provide optimized desired performance properties. This is a significant improvement over conventional PCD or PCBD compositions, not having a surface structure configuration of ordered material phases, that provide relatively limited performance properties due to the compromise inherent in the materials and manner of construction.